1. Field of the Invention
The present invention generally relates to a compressor control system for use with a compressor associated with a natural gas producing well or wells in which the compressor is automatically shutdown in response to certain conditions, automatically unloaded when shutdown, automatically restarted in response to certain shutdown conditions with re-starting of the compressor including the retention of the compressor in an unloaded condition for a predetermined time interval with the system also including a control for the inlet pressure for maintaining a desired flow rate from the compressor regardless of fluctuations in upstream conditions.
2. Description of the Prior Art
The transfer of natural gas from low pressure wells to high pressure pipelines for delivery to users has presented many problems primarily due to fluctuations in the well pressure and flow rate and fluctuations in pipeline pressure. Compressors have been used for this purpose with the compressors being powered by various types of motors such as electric motors, internal combustion engines, and the like. When such compressors are utilized, it is necessary to provide automatic shutdown features to stop the compressor under certain conditions which, if the compressor continued to operate, would produce adverse and in some instances, dangerous results.
U.S. Pat. No. 3,407,052, issued Oct. 22, 1968 to Huntress et al, discloses a compressor utilized in a natural gas liquefaction system rather than a gas transmission or transfer system and the compressor is not provided with a given flow rate even though the inlet pressure may be variable and does not include an automatic shutdown and unloading and automatic re-start of the compressor in response to inlet or outlet pressures.
U.S. Pat. No. 3,837,377, issued Sept. 24, 1974 to McJones, discloses a system to prevent over-pressurizing a natural gas cylinder and automatically closes a fill line when a predetermined volume is reached in the cylinder which is a different concept from this invention.
U.S. Pat. No. 3,975,115, issued Aug. 17, 1976 to Fisher et al, discloses a pump control system which is pilot operated but does not utilize a control sensitive to inlet or discharge pressure variations and there is no volume control.
U.S. Pat. No. 3,985,467, issued Oct. 12, 1976, to Lefferson, discloses a sensing device to maintain a constant fluid pressure for a variable speed motor which utilizes a feedback network to provide a constant discharge pressure.
U.S. Pat. No. 4,213,476, issued July 22, 1980 to Bresie et al, discloses a compressor having a bypass arrangement which becomes effective when a predetermined maximum discharge pressure is reached. This patent does not have an automatic shutdown and re-start arrangement nor is the compressor unloaded when it is shutdown. This patent also discloses a well control pressure regulating device which is not associated with the compressor.
U.S. Pat. No. 4,218,191, issued Aug. 19, 1980 to Stewart, discloses a compressor having a constant inlet pressure accomplished by a variable speed prime mover with this system being primarily for the purpose of maintaining a low pressure on another system rather than for natural gas transfer or transmission.